1. Field of the Invention
The present invention relates to a taper-etching method for forming a groove having a V-shaped cross section in an SiO2 or SiON layer to be etched, and to a method of manufacturing a near-field light generator using the taper-etching method.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
U.S. Patent Application Publication No. 2010/0290323 A1 discloses a technology for coupling the light that propagates through the waveguide with the plasmon generator in surface plasmon mode via a buffer part, thereby exciting surface plasmons on the plasmon generator.
Here, a description will be given of an example of the shape of the plasmon generator and the arrangement of the plasmon generator and the waveguide. In this example, the plasmon generator is disposed above the top surface of the core of the waveguide. The plasmon generator has an edge part facing the top surface of the core of the waveguide. A clad is disposed around the core. The clad includes a part lying between the edge part of the plasmon generator and the top surface of the core, and this part of the clad serves as the buffer part.
In the aforementioned plasmon generator, an end of the edge part located in the medium facing surface serves as a near-field light generating part. In the plasmon generator, the light that propagates through the core is totally reflected at the top surface of the core. This causes evanescent light to occur from the top surface of the core. Then, at least on the edge part of the plasmon generator, surface plasmons are excited through coupling with the foregoing evanescent light. The surface plasmons propagate along the edge part to reach the near-field light generating part, and near-field light is generated from the near-field light generating part based on the surface plasmons. Such a configuration allows the surface plasmons excited on the plasmon generator to propagate to the near-field light generating part with high efficiency.
The aforementioned configuration can be formed in the following manner. First, a layer to be etched is formed using a dielectric material that is to be employed for the clad. Part of the layer to be etched is located on the top surface of the core. Then, a groove that is V-shaped in cross section parallel to the medium facing surface (hereinafter, also referred to as V-shaped groove) is formed in the layer to be etched. This groove is formed not to reach the top surface of the core. Being provided with the groove, the layer to be etched becomes part of the clad. The plasmon generator is then formed in the groove.
In the aforementioned configuration, the V-shaped groove has two wall faces that intersect at a predetermined angle, and the plasmon generator has two inclined surfaces that are opposed to the two wall faces. The edge part of the plasmon generator is defined by the two inclined surfaces of the plasmon generator intersecting each other. The angle formed by the two inclined surfaces affects the intensity of surface plasmons excited on the plasmon generator and the spot diameter of the near-field light generated from the near-field light generating part. As the angle formed by the two inclined surfaces decreases, the edge part becomes sharper and the near-field light generated from the near-field light generating part decreases in spot diameter. To increase the intensity of the surface plasmons excited on the plasmon generator, however, it is preferred that the angle formed by the two inclined surfaces be large to some extent. This means that there is a preferred range for the angle formed by the two inclined surfaces. By way of example, the angle formed by the two inclined surfaces preferably falls within the range of 50° to 120°. The angle formed by the two inclined surfaces can be defined within the range of 50° to 120° by allowing each of the two wall faces of the V-shaped groove to form an angle (hereinafter referred to as inclination angle) within the range of 30° to 65° with respect to the top surface of the layer to be etched, and allowing the angle between the two wall faces to fall within the range of 50° to 120°.
To form the V-shaped groove in the layer to be etched which will later become part of the clad, the layer to be etched can be taper-etched by reactive ion etching (hereinafter, also referred to as RIE). Generally in this method, an etching mask made of a photoresist is provided on the layer to be etched, and this etching mask is used to taper-etch the layer to be etched. For the taper-etching by RIE, the inclination angle of the wall faces of the groove depends on the ratio between the deposition rate of a sidewall protective film that is formed by a reaction product during the etching and the etching rate.
On the other hand, SiO2 (silicon dioxide) or SiON (silicon oxynitride) may be used as the material of the clad. In this case, it is required that a layer to be etched that is made of SiO2 or SiON be taper-etched by RIE to form therein the V-shaped groove with the inclination angle of each of the two wall faces defined within the range of 30° to 65°. However, under the conventional RIE method using an etching mask made of a photoresist, it is difficult to accomplish the taper-etching of the layer to be etched that is made of SiO2 or SiON to form therein the above-described V-shaped groove. More specifically, the conventional method can hardly form any groove or can form a bottomed groove whose two wall faces form an inclination angle of nearly 90° and do not intersect at a predetermined angle. This is presumably because the conventional method cannot form a sidewall protective film at an appropriate deposition rate during the etching.